Borophosphate phosphor and light source

ABSTRACT

This invention is related to efficient inorganic borophosphate phosphors which can applied in various technical applications such as fluorescent lamps, colored light or white light emitting diodes, and other devices where phosphors are used to convert especially near UV radiation into the visible light. Further, this invention is related to light sources comprising the efficient borophosphate phosphor. The inventive phosphor absorbs radiation in a first wavelength range of the electromagnetic spectrum and emits radiation in a second wavelength range of the electromagnetic spectrum. This phosphor is a borophosphate activated with divalent rare earth metal ions.

BACKGROUND OF THE INVENTION

This invention is related to efficient inorganic borophosphate phosphors which can applied in various technical applications such as fluorescent lamps, colored light or white light emitting diodes, and other devices where phosphors are used to convert especially near UV radiation into the visible light. Further, this invention is related to light sources comprising the efficient borophosphate phosphor.

In the solid-state lighting industry, the wavelength conversion phosphor materials play a crucial role as they once did in fluorescent lamps. White LED lighting within a phosphor converted-LED (pc-LED) system can be realized by several approaches: The first approach is to combine the InGaN based blue-LED chip (emitting blue light between 455 nm and 465 nm with a yellow phosphor, i.e., YAG:Ce³⁺ or EA₂SiO₄:Eu²⁺ based materials. However, the white LED provided by this well known and established method has the disadvantages of poor color rendering when used for general lighting and small color gamut when used for backlighting. The second one is to combine a blue-LED chip with a green-emitting phosphor (λ_(max)˜530 nm) and a red-emitting phosphor (λ_(max)>600 nm) instead of the single yellow-emitting phosphor. The two phosphors absorb the blue light from the InGaN chip and convert it into green and red light and then by color mixing the white light is generated with higher color rendering and larger color gamut. But in both methods the final color temperature (CCT) and color coordinate of the pc-LED strongly depends on the emission characteristics of the blue-LED chips. As a consequence, in order to get a similar CCT only a part of available blue-LED chips can be used. The third one is to use a near UV-LED chip plus blue, green, and red emitting phosphor. In comparison with the former two ways, the third one provides improved color rendering and a wide range of color temperatures as well as an independent color coordinate. The disadvantage of this technical solution is the color shift during the life cycle resulting from the different aging rate of the three different phosphors.

There are also attempts to provide phosphors that are excitable by a radiation source of the near UV and emit the visible light, especially, a single phosphor which can emit white light without the request to combine with some other phosphors. Its emission spectrum is composed of the three primary colors (blue, green, and red) and covers the whole visible range from 400 nm to 700 nm. Subsequently, some of these attempts are cited:

In the article of Park et al. in Appl. Phys. Lett. 82 (2004) pages 2931-2933; Solid state comm. 136 (2005) 504, a phosphor of the general formula: EA₃MgSi₂O₈:Eu²⁺, Mn²⁺ (EA=Sr, Ba) is presented. This phosphor shows three emission bands peaking at 422 nm, 505 nm and 620 nm. The 442 nm and 505 nm emissions originate from Eu²⁺, while the 620 nm emission originates from Mn²⁺ ions. The fabricated white light emitting light diode integrating 400-nm-emitted chip with EA₃MgSi₂O₈:Eu²⁺, Mn²⁺ (EA=Sr, Ba) phosphor shows warm white light and higher color rendering index and higher color stability against input power in comparison with a commercial blue-pumped YAG:Ce³⁺. However, this white LED has a low luminous efficiency and a poor long-term stability.

In J. Electrochem. Soc. 155 (2008) pages J 193-J 197; Electrochem. Solid state lett. 11 [2] (2008) E1, white light emitting phosphor has been proven to be a mixture of EA₃MgSi₂O₈:Eu²⁺, Mn²⁺ (EA=Sr, Ba) and EA₂SiO₄:Eu²⁺ (EA=Ba, Sr). In fact, the emission band peaking at 505 nm originates from EA₂SiO₄:Eu²⁺ (EA=Ba, Sr) instead of EA₃MgSi₂O₈:Eu²⁺, Mn²⁺ (EA=Sr, Ba).

In the article by Lakshminarasimhan et al. in J. electrochem. Soc. 152 [9] (2005) H152, systems of the formula Sr₂SiO₄:Eu,Ce are suggested. This system exhibits a low efficiency and poor stability.

In the article by Chang et al. in Appl. Phys. Lett. 90 (2007) 161901) systems of the formula Ca₂MgSi₂O₇:Eu,Mn. This system also exhibits a low efficiency and poor stability.

In the article of J. Liu et al. in Adv. Mater. 17 (2005) pages 2974-2978, a single phosphor is presented that can emit the blue (445 nm), green (515 nm), and red (624 nm) light simultaneously. The CIE coordinates are located at (0.31, 0.34), which is very close to (0.33, 0.33) of the standard white emission. The host lattice is an organic compound, which is not very stable under high temperature.

WO 2006/111568 A2 shows white light emitting non-stoichiometric compounds having a not fixed composition.

Recently, in the search for new functional materials, borophosphate, which contain both the borate group and the phosphate group as basic structural units, has also drawn attention. In the last couple of years many borophosphates were synthesized and structurally characterized. As far as luminescence is concerned, most of work has been focused on studying the luminescence properties of rare earth ions in MBPO₅ (M=Ca, Sr, Ba), (Ba, Sr)₃BP₃O₁₂, and (Ba, Sr)₆BP₅O₂₀Ba₃BPO₇ host lattices.

DE 1 927 455 shows borate phosphate phosphors like Ba_(0.995)Eu_(0.005)BPO₅ and Sr_(0.99)Eu_(0.01)BPO₅ that are used in low-pressure mercury discharge lamps. These Eu²⁺-activated MBPO₅ phosphors show a broad emission band in the UV to blue range with a maximum, dependent on the alkaline earth metals present, at 385 nm to 400 nm.

DE 29 00 989 A1 shows borate phosphate phosphors of the general formula Ba_(3-p)Eu_(p)BP₃O₁₂ for the usage in low-pressure mercury discharge lamps. These phosphors show a greenish emission with the maximum in the wavelength range of 490 nm to 520 nm.

In Appl. Phys. B 86 (2007), Pages 647-651, Eu²⁺-activated (Ba,Sr)₆BP₅O₂₀ phosphors are shown that exhibit bluish green emission in the wavelength range of 470 nm to 510 nm.

A new kind of borophosphate, i.e. KMBP₂O₈ (M=Ba, Sr), was discovered by Zhao et al. [Inorg. Chem. 48 (2009) pages 6623-6629] in 2009. Until now, the luminescence properties of the rare earth ions in these host lattices have never been reported. The main structure features of this host lattice are similar to those of the other borophosphate compounds, i.e. a network of PO₄ tetrahedron and BO₃ triangles/BO₄ tetrahedrons.

WO 2009/036425 A1 shows a phosphor blend for a compact fluorescent lamp comprising LaPO₄:Ce³⁺, Tb³⁺; Y₂O₃:Eu³⁺; Sr₆BP₅O₂₀:Eu²⁺ and Mg₄GeO_(5.5)F:Mn⁴⁺.

BRIEF SUMMARY OF THE INVENTION

An object of this invention is to provide improved phosphors that are excitable by a radiation source of the near UV and emit the visible light, especially, as a single phosphor which can emit white light without the request to combine with some other phosphors. A further object is to provide an appropriate light source.

These objects are achieved by an inventive phosphor according to claim 1 and by an inventive light source according to claim 13.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows typical powder XRD patterns of KBa_(1-x)Eu_(x)BP₂O₈ (x=0.05);

FIG. 2 shows typical excitation and emission spectra of KBa_(1-x)Eu_(x)BP₂O₈ (x=0.05);

FIG. 3 shows temperature dependent luminescence of Eu²⁺-doped KBaBP₂O₈;

FIG. 4 shows emission spectra of KBa_(1-x)Eu_(x)BP₂O₈ phosphor with different Eu²⁺ doping concentrations;

FIG. 5 shows typical XRD patterns of Eu²⁺-doped K(Ba,Sr)BP₂O₈ and K(Ba,Ca)BP₂O₈ phosphors;

FIG. 6 shows excitation (inset) and emission spectra of Eu²⁺-doped K(Ba,Sr)Eu_(0.03)BP₂O₈ with different Sr and Ba contents;

FIG. 7 shows excitation (inset) and emission spectra of Eu²⁺-doped K(Ba,Ca)Eu_(0.03)BP₂O₈ with different Ca and Ba contents;

FIG. 8 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ partly substituted by Na;

FIG. 9 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ partly substituted by Li; and

FIG. 10 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ partly substituted by Zn.

DETAILED DESCRIPTION

Surprisingly, single Eu²⁺-activated KMBP₂O₈ (M=Ba, Sr, Ca) phosphors show white light with high luminous efficiency under near UV excitation. The behavior is unexpected because all other borophosphate phosphors have never shown such a luminescence property and because there is only one crystallographic site available for the activator Eu²⁺. In addition, they exhibit a high thermal stability, which is comparable to that of YAG:Ce³⁺ phosphor. The luminescence properties (e.g. peak center, color coordination and FWHM) of Eu²⁺-doped KMBP₂O₈ phosphors can be adjusted by changing the Eu²⁺ concentration or the ratio between Ba, Sr and Ca in KMBP₂O₈ host lattice. The Eu²⁺ concentration can vary in a wide range. The emission band of Eu²⁺-doped KBaBP₂O₈ phosphor can be shifted to the longer wavelength range by increasing the Eu²⁺ concentration. While the emission bands of Eu²⁺-doped KBaBP₂O₈ phosphors can be shifted to the shorter wavelength range by the replacement of Ba²⁺ by Sr²⁺. In addition, its luminous efficiency also can be improved dramatically by such a replacement. The same effect also can be reached by the replacement of Ba²⁺ by Ca²⁺. In all the Eu²⁺-doped phosphors, it would expect that Eu²⁺ will replace the crystallographic site of M²⁺ with 8-fold oxygen coordination.

The present invention discloses new borophosphate phosphors that are activated by rare earth ions, preferably by Eu²⁺ ions.

The inventive phosphor converts radiation. For this, it absorbs radiation in a first wavelength range of the electromagnetic spectrum and emits radiation in a second wavelength range of the electromagnetic spectrum. The first wavelength range of the electromagnetic spectrum differs from the second wavelength range of the electromagnetic spectrum.

The inventive borophosphate phosphor is activated with divalent rare earth metal ions. It is represented by the following general formula: AM_(1-x)RE_(x)BP₂O₈

Symbol A represents at least one univalent alkaline metal ion. Symbol M stands for at least one divalent metal ion. Symbol RE is at least one divalent ion selected from the group comprising rare earth metals as well as Pb, Sn, Cu, and Mn. Anyway, RE contains at least one divalent rare earth metal ion that is acting as an activator. Variable x is limited by 0<x<1.

Preferably, RE contains at least the divalent rare earth metal ion of Eu, namely Eu²⁺ that is acting as activator.

In a further preferred embodiment, RE contains at least the divalent rare earth metal ion of Sm or Yb, namely Sm²⁺ or Yb²⁺ that is acting as activator.

Preferably, RE further contains at least one divalent ion selected from the group comprising Ce, Yb, Tb, Gd, Dy, and Sm that is acting as a coactivator. Alternatively or supplementary, RE further contains at least one divalent ion selected from the group comprising Pb, Sn, Cu, and Mn that is acting as a coactivator.

Variable x is preferably less than or equal to 0.2; and more preferably less than or equal to 0.1.

In a preferred embodiment, symbol A represents at least one univalent alkaline metal ion selected from the group comprising Li, K, Na, Rb, and Cs; or more preferably, selected from the group comprising Li, K, and Na.

Preferably, M stands for at least one divalent metal ion selected from the group comprising Ca, Sr, Ba, Be, Mg, and Zn; or more preferably, selected from the group comprising Ca, Sr, and Ba.

In a preferred embodiment of the invention, the phosphor shows the following formula: AM_(1-x)EU_(x)BP₂O₈ wherein A=Li, K, Na, Rb, and/or Cs; and wherein M=Ca, Sr, Ba, Be, Mg, and/or Zn.

In a further preferred embodiment of the inventive phosphor, symbol A stand for potassium K. Further, symbol M represents at least one divalent metal ion selected from the group comprising Ca, Sr, Ba, and Zn. RE contains at least one divalent rare earth metal ion selected from the group comprising Eu, Sm, and Yb that is acting as activator and at least one divalent ion selected from the group comprising Pb, Cu, and Mn. In this embodiment, variable x is less than or equal to 0.1.

In a further preferred embodiment of the invention, M stands for calcium, barium, strontium, or combinations of these three elements resulting in one of the following formulae: ABa_(1-x)EU_(x)BP₂O₈; ABa_((1-x-y))Sr_(y)EU_(x)BP₂O₈; and ABa_((1-x-z))Ca_(z)Eu_(x)BP₂O₈; wherein 0≦y≦1.0 and 0≦z≦0.3.

Preferably, A is at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na. Further, M stands for Ba. RE represents Eu. Variable x is smaller or equal 0.1. The resulting general formula is: ABa_(1-x)Eu_(x)BP₂O₈.

In that embodiment, A is preferably K, resulting in the general formula: KBa_(1-x)Eu_(x)BP₂O₈, wherein variable x is more preferably less than or equal to 0.08.

In another preferred embodiment of the invention, symbol A stands for at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na. Further M consists of Ba and Sr. RE represents Eu. The resulting general formula is: Aba_((1-x-y))Sr_(y)Eu_(x)BP₂O₈, wherein x≦0.1, 0<y<1.0 and (x+y)<1.0. In this embodiment, A is preferably K, resulting in the general formula: KBa_((1-x-y))Sr_(y)EU_(x)BP₂O₈, wherein variable x is more preferably less than or equal to 0.08 and y is more preferably less than or equal to 0.4, wherein (x+y)≦0.5.

In another preferred embodiment of the invention, symbol A stands for at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na. Further M consists of Ba and Ca. RE represents Eu. The resulting general formula is: ABa_((1-x-z))Ca_(z)Eu_(x)BP₂O₈, wherein x≦0.1 and 0<z≦0.3. In this embodiment, A is preferably K, resulting in the general formula KBa_((1-x-z))Ca_(z)Eu_(x)BP₂O₈, wherein variable x is more preferably less than or equal to 0.08 and wherein (x+z)≦0.3.

The inventive phosphor shows a strong excitation band in the wavelength range of 250 nm to 420 nm. From there, the first wavelength range ranges preferably from 250 nm to 420 nm; or more preferably from 300 nm to 370 nm.

The second wavelength range is preferably the whole visual spectrum, especially in the range from 400 nm to 700 nm, or at least in the range from 420 nm to 600 nm. A peak center of the second wavelength is preferably between 450 nm and 480 nm.

The inventive phosphor can be well excited under UV light irradiation and emits blue or white light. In addition, the phosphor shows high thermal stability, which is comparable to that of YAG:Ce³⁺ phosphor.

Due to the described luminescence characteristics, the phosphor according to the present invention can be used as a radiation converter for the transformation of UV (250 nm to 420 nm) into a longer-wave visible light that well be emitted by the phosphor preferably in blue to orange spectral region.

The inventive phosphor can be used in light sources, e.g. in white light emitting light sources. Alternatively, this phosphor can be used in photovoltaic cells, in greenhouse foils, or in greenhouse glasses. In these applications, the light of the Sun forms the radiation in the first wavelength range of the electromagnetic spectrum. The radiation emitted by the phosphor will be directed to the photovoltaic cells and to the plants in the greenhouse, respectively.

The inventive light source comprises an inventive phosphor and a radiation emitting element that emits radiation in the first wavelength range of the electromagnetic spectrum. The phosphor converts the emitted radiation of the first wavelength range into the radiation of the second wavelength range. The radiation emitting element acts as excitation source for the phosphor. The light source emits at least the radiation in the second wavelength range of the phosphor.

In a special embodiment of the inventive light source, the light source comprises at least one further phosphor that emits red, yellow, green, and/or blue light in order to improve the performance of the light source.

The inventive light source is preferably formed by a fluorescent lamp, by a colored light emitting LED, by a white light emitting LED or by an application based on UV laser or purple laser excitation.

The radiation emitting element is preferably formed by high-pressure discharge plasma or by low-pressure discharge plasma, by a UV inorganic light emitting diode (LED) or by a purple-blue inorganic light emitting diode (LED), or by a laser or by a laser diode. The radiation emitting element can be formed by an LED. This encloses different types of inorganic LED like SMD, top-LED, and side-view LED that are having a plastic or ceramic body and incorporating a light emitting element which emits radiation in the first wavelength range, especially; in the UV-A and purple-blue.

The luminescent borophosphate phosphor according to the invention can be prepared by means of a solid state reaction at a high temperature of a mixture of oxides of the component elements or compounds which are converted into the corresponding oxides on heating. In general, it is advantageous to heat the starting mixtures in two steps. The product obtained need to be pulverized after cooling after each heating operation. The last heating operation is usually performed in a reducing atmosphere (i.e. 70% N₂-30% H₂) to obtain the europium in the desired bivalent state.

In the following the synthesis conditions are still described in more detail on the basis of a few examples. The examples describe typical conditions and materials but do not act as limitation. Persons who skilled in the art may find some different ways to get the phosphor, e.g. substitution of raw materials by other decomposable salts, for instance; carbonates by oxalates, acetates, nitrates; using other mixing methods like ball mill, vibration mill and others; deviation in temperature, atmosphere and duration of the high temperature solid state reaction, application of sol-gel-processes or spray pyrolysis and others.

Example 1

A mixture is made of 1.380 g K₂CO₃, 4.020 g BaCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃ and 4.601 g NH₄H₂PO₄. The raw materials were weighted in an agate mortar and homogenously mixed. This mixture was placed in alumina crucibles. The crucibles covered with an alumina plate were heated in a furnace in air for 4 hours at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 8 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula KBa_(0.97)Eu_(0.03)BP₂O₈ was obtained. For X-ray diffraction photograph, it appeared that the crystalline powder had the crystal structure of the KBaBP₂O₈ phase.

Example 2

A mixture is made of 1.380 g K₂CO₃, 2.644 g BaCO₃, 0.886 g SrCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 10 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula KBa_(0.67)Sr_(0.30)Eu_(0.03)BP₂O₈ was obtained. For X-ray diffraction photograph, it appeared that the crystalline powder had the crystal structure of the KBaBP₂O₈ phase. The luminescence intensity of the sample is about 135% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 3

A mixture is made of 1.380 g K₂CO₃, 3.236 g BaCO₃, 0.300 g CaCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 6 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 12 hour at 900° C. under flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula KBa_(0.82)Ca_(0.15)Eu_(0.03)BP₂O₈ was obtained. For X-ray diffraction photograph, it appeared that the crystalline powder had the crystal structure of the KBaBP₂O₈ phase. The luminescence intensity of this sample is about 126% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 4

A mixture is made of 1.106 g K₂CO₃, 0.202 g Na₂CO₃, 3.828 g BaCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 9 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula K_(0.8)Na_(0.2)Ba_(0.97)Eu_(0.03)BP₂O₈ was obtained. The luminescence intensity of the sample is about 120% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 5

A mixture is made of 1.106 g K₂CO₃, 0.148 g Li₂CO₃, 3.828 g BaCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 9 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula K_(0.8)Li_(0.2)Ba_(0.97)Eu_(0.03)BP₂O₈ was obtained. The luminescence intensity of the sample is about 80% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 6

A mixture is made of 1.382 g K₂CO₃, 0.163 g ZnO, 3.434 g BaCO₃, 0.106 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 9 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula KBa_(0.87)Zn_(0.1)Eu0_(.03)BP₂O₈ was obtained. The luminescence intensity of the sample is about 105% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 7

A mixture is made of 1.382 g K₂CO₃, 0.070 g Sm₂O₃, 3.710 g BaCO₃, 0.140 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 9 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula K_(0.8)Li_(0.2)Ba_(0.97)Eu_(0.03)BP₂O₈ was obtained. The luminescence intensity of the sample is about 98% relative to that of the sample in Example 1 under excitation of 340 nm.

Example 8

A mixture is made of 1.382 g K₂CO₃, 0.078 g Yb₂O₃, 3.710 g BaCO₃, 0.140 g Eu₂O₃, 1.298 g H₃BO₃, and 4.601 g NH₄H₂PO₄. This mixture was heated for 4 h in a furnace in air at a temperature of 400° C. After cooling and pulverizing, the product was subjected to a heat operation for 9 hour at 900° C. under a flowing 70% N₂-30% H₂ atmosphere in a covered alumina crucible. After cooling and pulverizing, a luminescent materials have a composition defined by the formula KBa_(0.94)Eu_(0.04)Yb_(0.02)BP₂O₈ was obtained. The luminescence intensity of the sample is about 85% relative to that of the sample in Example 1 under excitation of 340 nm.

In the following table, luminescence properties of Eu²⁺-doped KBaBP₂O₈ phosphors with different Eu²⁺ doping concentrations are listed:

Rela- Peak tive cen- Color inten- ter coordination FWHM sity Samples KBa_(1−x)Eu_(x)BP₂O₈ (nm) x y (nm) (%) BP 0009  x = 0.005 454.5 0.2342 0.2877 146 71 BP 0010 x = 0.01 461.6 0.2312 0.2919 145 94 BP 0011 x = 0.02 464.5 0.2323 0.2999 144 98 BP 0012 x = 0.03 468.2 0.2275 0.2914 139 100 BP 0013 x = 0.05 468.8 0.2410 0.3105 147 94 BP 0014 x = 0.08 468.0 0.2419 0.3317 147 87 BP 0015 x = 0.10 474.6 0.2407 0.3174 148 60

In the following table, luminescence properties of Eu²⁺-doped KBa_(1-y)Sr_(y)BP₂O₈ (0≦y≦1.0) phosphors with different Sr contents are listed:

Peak Color Relative center coordination FWHM intensity Samples KBa_(0.97−y)Sr_(y)Eu_(0.03)BP₂O₈ (nm) x y (nm) (%) BP 0012 y = 0   468.2 0.2275 0.2914 139 100 BP 0027 y = 0.05 466.3 0.2238 0.2861 132 107 BP 0028 y = 0.10 462.5 0.2152 0.2699 122 119 BP 0029 y = 0.15 458.3 0.2081 0.2556 114 127 BP 0030 y = 0.20 458.4 0.2054 0.2488 110 130 BP 0031 y = 0.25 457.7 0.2020 0.2421 106 132 BP 0032 y = 0.30 458.1 0.1988 0.2353 102 135 BP 0033 y = 0.50 456.3 0.1904 0.2181 93 130 BP 0047 y = 0.97 454.5 0.1906 0.2067 91 73

In the following table, luminescence properties of Eu²⁺-doped KBa_(1-z)Ca_(z)BP₂O₈ (0≦z≦0.30) phosphors with different Ca contents are listed:

Peak Color center coordination FWHM Relative Samples KBa_(0.97−z)Ca_(z)Eu_(0.03)BP₂O₈ (nm) x y (nm) intensity (%) BP 0012 z = 0   468.2 0.2275 0.2914 139 79 BP 0020 z = 0.03 463.3 0.2230 0.2848 131 100 BP 0021 z = 0.05 461.5 0.2178 0.2736 124 106 BP 0022 z = 0.10 458.9 0.2049 0.2450 108 119 BP 0023 z = 0.15 453.9 0.1972 0.2270 99 127 BP 0025 z = 0.30 450 0.1957 0.2193 95 101

The foregoing and other features and advantages of the present invention will become more readily appreciated as the same become better understood by reference to the following accompanying drawings, wherein:

FIG. 1 shows typical powder XRD patterns of KBa_(1-x)Eu_(x)BP₂O₈ (x=0.05), namely KBa_(0.95)Eu_(0.05)BP₂O₈ in comparison to KBaBP₂O₈.

FIG. 2 shows typical excitation and emission spectra of KBa_(1-x)Eu_(x)BP₂O₈ (x=0.05), namely KBa_(0.95)Eu_(0.05)BP₂O₈.

FIG. 3 shows temperature dependence of the luminescence of Eu²⁺-doped KBaBP₂O₈ phosphor under excitation of 405 nm in comparison to YAG:Ce³⁺.

FIG. 4 shows emission spectra of KBa_(1-x)Eu_(x)BP₂O₈ phosphor with different Eu²⁺ doping concentrations ranging from x=0.005 to x=0.10.

FIG. 5 shows typical XRD patterns of KBa_(0.67)Ca_(0.3)Eu_(0.03)BP₂O₈, KBa_(0.87)Ca_(0.1)Eu_(0.03)BP₂O₈, and KBa_(0.77)Sr_(0.2)Eu_(0.03)BP₂O₈ in comparison to KBaBP₂O₈ and KSrBP₂O₈.

FIG. 6 shows excitation (inset) and emission spectra of KBa_(0.97)Eu_(0.03)BP₂O₈, KBa_(0.87)Sr_(0.1)Eu_(0.03)BP₂O₈, KBa_(0.77)Sr_(0.2)Eu_(0.03)BP₂O₈, KBa_(0.67)Sr_(0.3)Eu_(0.03)BP₂O₈, and KSr_(0.97)Eu_(0.03)BP₂O₈.

FIG. 7 shows excitation (inset) and emission spectra of KBa_(0.97)Eu_(0.03)BP₂O₈, KBa_(0.92)Ca_(0.05)Eu_(0.03)BP₂O₈, KBa_(0.87)Ca_(0.1)Eu_(0.03)BP₂O₈, KBa_(0.82)Ca_(0.15)Eu_(0.03)BP₂O₈, and KBa_(0.67)Ca_(0.3)Eu_(0.03)BP₂O₈.

FIG. 8 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ and in the case when K is partly substituted by Na.

FIG. 9 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ and in the case when K is partly substituted by Li.

FIG. 10 shows emission spectra of Eu²⁺-doped KBaBP₂O₈ and in the case when Ba is partly substituted by Zn. 

The invention claimed is:
 1. A phosphor that absorbs radiation in a first wavelength range of the electromagnetic spectrum and emits radiation in a second wavelength range of the electromagnetic spectrum, wherein the phosphor is a borophosphate activated with divalent rare earth metal ions and represented by the following general formula: AM_(1-x)R_(x)BP₂O₈; wherein: A is at least one univalent alkaline metal ion selected from the group comprising Li, K, Na, Rb, and Cs; M is at least one divalent metal ion selected from the group comprising Ca, Sr, Ba, Be, Mg, and Zn; RE is at least one divalent ion selected from the group comprising rare earth metals Eu, Sm, and Yb as well as Pb, Sn, Cu, and Mn, wherein at least one of the divalent rare earth metal ions Eu, Sm, and/or Yb is acting as an activator; and 0<x≦0.2.
 2. The phosphor of claim 1, wherein RE contains at least the divalent rare earth metal ion of Eu that is acting as activator.
 3. The phosphor of claim 1, wherein RE further contains at least one divalent ion selected from the group comprising Yb and/or Sm that is acting as a coactivator.
 4. The phosphor of claim 1, wherein A is K; wherein M is at least one divalent metal ion selected from the group comprising Ca, Sr, Ba, and Zn; wherein RE contains at least one divalent rare earth metal ion selected from the group comprising Eu, Sin and Yb that is acting as activator and at least one divalent ion selected from the group comprising Pb, Cu, and Mn; and wherein x≦0.1.
 5. The phosphor of claim 2, wherein A is at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na; wherein M is Ba; wherein RE is Eu; and wherein x≦0.1, resulting in the general formula: ABa_(1-x)Eu_(x)BP₂O₈.
 6. The phosphor of claim 5, wherein A is K, resulting in the general formula: KBa_(1-x)Eu_(x)BP₂O₈.
 7. The phosphor of claim 2, wherein A is at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na; wherein M consists of Ba and Sr; wherein RE is Eu; and wherein x≦0.1, 0<y<1.0 and (x+y)<1.0, resulting in the general formula: ABa_((1-x-y))Sr_(y)Eu_(x)BP₂O₈.
 8. The phosphor of claim 7, wherein A is K, resulting in the general formula: KBa_((1-x-y))Sr_(y)Eu_(x)BP₂O₈.
 9. The phosphor of claim 2, wherein A is at least one univalent alkaline metal ion selected from the group comprising Li, K, and Na; wherein M consists of Ba and Ca; wherein RE is Eu; and wherein x≦0.1 and 0<z≦0.3; resulting in the general formula: ABa_((1-x-z))Ca_(z)Eu_(x)BP₂O₈.
 10. The phosphor of claim 9, wherein A is K, resulting in the general formula: KBa_((1-x-z))Ca_(z)Eu_(x)BP₂O₈.
 11. The phosphor of claim 1, wherein the first wavelength range ranges from 250 nm to 420 nm.
 12. The phosphor of claim 1, wherein the second wavelength range is the whole visual spectrum.
 13. A light source comprising a phosphor according to claim 1 and a radiation emitting element that emits radiation in the first wavelength range of the electromagnetic spectrum. 